The present invention relates to a load engaging apparatus for use with material handling equipment and, more particularly, to controls for transversely movable load engaging members such as forks or clamp arms of a load engaging apparatus associated with material handling equipment.
Material handling equipment used for moving palletized or non-palletized loads from place to place, such as, for example, in a warehouse, typically includes forklift trucks or other types of material handling equipment equipped with load engaging members such as forks or clamp arms. For example, on a typical forklift truck load engaging forks are attached to a carriage which is in turn movably secured in a mast so as to enable the carriage and forks to travel vertically in the mast. Various types of attachments may also be mounted on the carriage or integrated with the carriage. For example, a sideshifter which moves the forks transversely in unison and/or a fork positioner which enables movement of the forks transversely toward and away from each other may be either attached to the carriage or integrated with the carriage structure. Likewise, a load clamp having load-engaging clamp arms similarly movable transversely in unison either toward or away from each other may be attached to the carriage or integral to the carriage. Some attachments also include amotor enabling rotation of the load engaging members and thereby the load about an axis substantially parallel to the longitudinal axis of the material handling equipment.
Load clamps rely on clamping forces applied to the sides of the load for securing the load for lifting and clamp arms may be engineered differently for handling rectangular or cylindrical loads. For example, paper roll clamps and drum-clamping forks may incorporate contours particularly useful for clamping cylindrical loads. On the other hand, “carton clamps” generally refers to clamps with clamp arms adapted to handle rectangular loads such as stacked cartons or household appliances. Carton clamp attachments typically include a pair of large blade-shaped clamp members each of which can be inserted between side-by-side stacks of cartons or appliances to bracket a load comprising one or more appliances or cartons. The clamp members on either side of the load are then drawn together, typically, using hydraulic cylinders to move the clamp members and to apply sufficient compressive force to the load to allow it to be lifted. To securely hold the load, the surfaces of the clamp members which contact the sides of the load are typically constructed of materials such as rubber faced aluminum providing a high coefficient of friction. Carton clamps are most frequently used in the warehousing, beverage, appliance, and electronics industries and may be specifically designed for particular types of loads. For example, carton clamps may be equipped with contact pads that are sized for palletless handling of refrigerators, washers, and other large household appliances (also referred to as “white goods”). In various configurations, carton clamps may be used for handling multiple appliances at one time.
In addition to clamping a load in order to lift and move the load, clamps may be equipped with side-shifting capabilities whereby the clamped load may be repositioned from side-to-side with the clamping members moving transversely in one direction or the other in unison. Similarly, a fork positioner enabling transverse movement of load supporting forks to increase or decrease the distance between the forks may also include side-shifting enabling transverse movement of the forks in unison. When the longitudinal axis of the material handling vehicle is not perfectly aligned, transversely, with the center of a load, a stack or a rack space, side shifting can enable lateral alignment of the load engaging members, clamp arms or forks, with the load, stack or rack opening in which the load is to be engaged or deposited without further maneuvering of the vehicle. In addition, efficient utilization of space, notably when loading a transport vehicle, such as a trailer or railcar, commonly requires that loads be placed in close proximity to a wall or another obstacle. Side shifting allows loads that are narrower than the material handling vehicle to be placed close to a wall without first depositing the load and then pushing it, potentially, damaging it or the material handling vehicle. The side-shifting function may be actuated by one or more hydraulic cylinders separate from the clamping/fork positioning cylinder(s) (“external” side-shifting), or by the clamping/fork positioning cylinders themselves (“internal” side-shifting).
While side shifting is operationally advantageous, the off-center position of the load relative to the material handling vehicle adversely impacts the stability of the vehicle, particularly when the load is elevated. To compensate for the off-center weight of the load, a material handing vehicle may be “de-rated” and relegated to handling loads that are lighter than the nominal capacity load for the same vehicle when it is not equipped for side shifting. Conversely, a higher capacity, more expensive and less maneuverable material handing vehicle may be required to handle a load of a particular size or weight if the load can be side shifted.
What is desired, therefore, is a system and apparatus which optimizes the capability of a material handling vehicle equipped for side shifting.